Abstract Chronic ischemia induced tissue fibrosis contributes to numerous end-stage diseases. It is well accepted that macrophages play a major role in the generation of fibrotic tissues whereby dysregulated macrophage accumulation, activation, polarization and functions contribute to uncontrolled production of matrix metalloproteinases and extracellular matrix remodeling. Under pathological conditions, macrophages, along with fibroblasts and other cell types, serve as an initial and/or additional source of TGF-?1 and significantly contribute to the fibrosis. Moreover, endomyocardial biopsy specimens from patients with atherosclerotic coronary disease-induced ischemic cardiomyopathy demonstrated 45% of replacement fibrosis. Thus, identifying the signaling cascades in macrophage that regulates fibrosis in chronic ischemic diseases will have significant clinical benefit. MKP-5 has been implicated in innate immune responses, regenerative myogenesis and vascular inflammation. Our exciting preliminary data show that MKP-5 is upregulated in the fibrogenic zone of the heart. Genetic deletion of MKP-5 protects against early atherogenesis that leads to coronary artery insufficiency, decreases cardiac fibrosis and ameliorates ischemia-induced cardiac dysfunction in vivo. In vitro mechanistic studies and RNA-seq analysis suggested that loss of MKP-5 downregulated arrays of profibrogenic pathway genes including TGF-? signaling in macrophages and circulating monocytes. The central goal of this study is to identify the signaling cascades regulated by MKP-5 in macrophage that lead to tissue fibrosis. By using a novel chronic ischemia- induced cardiomyopathy model, we aim to: (1) interrogate the role of macrophage MKP-5 in ischemia-induced tissue fibrosis, (2) uncover the molecular mechanisms of macrophage MKP-5 in regulation of pro- and anti-fibrogenic signaling cascade, and (3) test the therapeutic potential of a newly developed MKP-5 allosteric inhibitor against fibrosis in vivo. We hypothesize that MKP-5 exacerbates tissue fibrosis through macrophage infiltration, polarization and TGF-? signaling. The success of proposed study will define the role of MKP-5 in regulating chronic ischemia-induced tissue fibrosis; provide proof-of-concept for applying MKP-5 inhibition for the management of this deadly disease.